They've tried it. The Twitter people come to Google+ looking for Twitter type engagement, but they don't find it. Likewise, the Facebook people come looking for Facebook-like engagement (family and friends) and don't find it.
It's like a Chinese tourist going to France looking for Chinese food and concluding that the food in France is terrible. Or a Hawaiian surfer bringing her surfboard to New York City and, finding no waves, concluding that there's nothing to do in Manhattan.
It's true: Google+ is not the best place to get the type of celebrity and pundit engagement you'd find on Twitter, or the updates from family and friends that you get on Facebook.
The truth is that Twitter and Facebook people are blind to the astonishing activity on Google+. So allow me to take you on a tour inside the Google+ world of interests and passions
Check out the incredible activity around baking bread, robots, quilting, drones, sushi, cosplay, fishing, motorcycles, scuba diving, ice cream, space, wedding dresses, coffee, martial arts, yoga, chocolate and tattoos. (Note: I picked these interests at random -- any passion will illustrate my point.)